Electromagnet system for a switch

ABSTRACT

An electromagnet system for a switch includes a main magnetic circuit including a magnet yoke and a magnet armature mechanically linked to a contact apparatus. At least one permanent magnet is disposed in the main magnetic circuit for generating a holding force for the magnet armature. A shunt circuit is provided parallel with the main magnetic circuit so that the permanent magnet is a magnetic energy source for the shunt circuit. The shunt circuit includes pole legs and a yoke arc of the magnet yoke. The magnet armature is capable of contacting the pole legs so as to close the shunt circuit. An excitation winding is provided for each of the pole legs for to generating a pull-in force for the magnet armature. The electromagnet system is magnetically dimensioned such that a minimum magnetomotive force of the excitation windings is sufficient for opening the electromagnet system.

The present invention relates generally to an electromagnet system for aswitch, and in particular to an electromagnet system for a switchcontactor, the electromagnet system including a main magnetic circuitformed by a magnet yoke and a magnet armature, and including a shuntcircuit which is closable via the magnet armature and is parallel to themain magnetic circuit.

BACKGROUND

Electromagnetic switch contactors are usually dimensioned electricallyand magnetically so that little electric power is to be applied in theholding state of the magnet armature (e.g., German Patent Application195 26 038 A1). This is recommended because devices of this type are inthe holding state most of their operating time. Power consumption in theholding state has the disadvantage that the device heats up. Powerlosses of a few watts are typically expected in the holding state. Forvacuum switchgears, considerably higher power losses may occur.Considering the fact that contactors or switches are mostly combined inone switch box, active measures for dissipating heat must be taken.

The use of electronics has not yet resulted in satisfactory improvement.Thus, known electronic approaches for electromagnet systems includecontrolling the power requirement via pulse width modulation. Thismethod results in the need for generating increasingly narrower pulsesin the circuit as power consumption decreases. As the pulses becomenarrower, harmonic components appear, which cause problems inelectromagnetic shielding and compatibility.

A magnet system having a circuit system for generating pulse trains toregulate power consumption is presented in German Patent Application 3910 810 A1 or in German Patent Application 195 26 038 A1, for example.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide anelectromagnet system in which the power loss in holding operation isreduced.

The present invention provides an electromagnet system for a switch. Theelectromagnetic switch includes: a main magnetic circuit including amagnet yoke and a magnet armature, the magnet armature being acted uponby a restoring device and being mechanically linked to a contactapparatus of the switch; at least one permanent magnet disposed in themain magnetic circuit and configured to generate a holding force for themagnet armature; a shunt circuit including a plurality of pole legs anda yoke arc of the magnet yoke, the yoke arc facing away from pole facesof the magnet yoke and being interrupted by a remanence air gap, themagnet armature being capable of contacting the pole legs so as to closethe shunt circuit, the shunt circuit being parallel with the mainmagnetic circuit so that the permanent magnet is a magnetic energysource for the shunt circuit; a circuit system configured toelectrically trigger the electromagnet system and to be operated in astand-by mode when the magnet armature contacts the pole legs; and atleast one excitation winding respectively associated with at least oneof the pole legs, an electromagnetic force of the at least oneexcitation winding being configured to generate a pull-in force for themagnet armature. The electromagnet system is magnetically dimensionedsuch that a minimum magnetomotive force of the at least one excitationwinding delivered by an energy accumulator to force a magnetic power ofthe permanent magnet into the shunt circuit is sufficient for openingthe electromagnet system.

The magnet system is based on the following structure:

-   a main magnetic circuit formed by a preferably U-shaped magnet yoke    and a magnet armature;-   a contact apparatus of the switch, mechanically linked to the magnet    armature, and a preferably spring-loaded magnet armature acted upon    by a restoring device;-   at least one permanent magnet situated in the main magnetic circuit    for generating the holding force for the magnet armature; and-   at least one excitation winding located on at least one pole leg,    i.e., on the magnet yoke, for generating the pull-in force for the    magnet armature isolated from the magnet yoke. The electromagnet    system is triggered electronically by an associated circuit system.

According to the present invention, parallel to the main magneticcircuit, a shunt circuit is provided, which is also closable via themagnet armature and the shunt circuit includes the two pole legs and asecond yoke arc, which is situated on the magnet yoke facing away fromthe pole faces and is interrupted by a remanence air gap.

Additional advantageous embodiments include the following:

The magnet system (magnet yoke, second yoke arc, and permanent magnet)is magnetically dimensioned such that the holding power—when the magnetarmature is pulled in—is applied by the permanent magnet alone withoutthe excitation winding being energized.

The permanent magnet generates a first magnetic force flux (MK1) via thepole legs and the magnet armature, and a second force flux (MK2) via theshunt circuit and the remanence flux gap. The absolute value of the twoforce fluxes is therefore determined by the state of charge of thepermanent magnet. The ratio of the force fluxes is determined by thedimensioning of the shunt circuit (including the remanence air gap) andthe distance of the magnet armature. The first magnetic force flux (MK1)is responsible for securely holding the magnet armature on the polefaces. This armature holding force counteracts the spring force whichopens the magnet system when there is little or no magnetic force. Inthis case, the magnet armature moves to stops, which are not shown. Theexcess armature holding force, generated via the magnetic flux by themagnet armature, over the spring force is a measure of the sensitivityof the magnet system to external mechanical interference. A minimummagnetomotive force (lowest current through the excitation coils,depending on the number of turns per unit length) should be sufficientfor opening the magnet system, whereby the first magnet flux is weakenedto the point that the spring force is sufficient to lift the magnetarmature. The above-mentioned low excitation current generates amagnetic flux which is opposite the flux through the magnet armature andwhich essentially displaces the first magnetic force flow into the shuntcircuit virtually without loss.

To close the magnet system, a considerably higher excitation current isused, which is sufficient to overcome the spring force at maximum magnetarmature stroke. As the magnet armature approaches the pole faces, themagnetic fluxes shift between the main and shunt flux circuits, whilethe magnetic energy remains constant.

The magnet yoke has a U-shaped design and has two L-shaped halves, eachhaving a longer pole leg and a shorter cross leg, one pole leg of eachhalf facing the contact faces of the magnet armature. The permanentmagnet is clamped in the center between the cross legs without welding.The second yoke arc is parallel to the cross legs.

The remanence air gap, whose width is on the order of magnitude of 0.3mm, may be filled with air or with a non-magnetic material.

The excitation winding of the magnet system is connected to an energyaccumulator, whose energy content is sufficient for releasing the magnetarmature from the holding state. The energy accumulator may be anaccumulator capacitor or an inductor.

A monitoring unit for controlling the voltage state of the energyaccumulator is preferably associated with the circuit system, whichmakes it possible to switch the system to another power source or tooutput an error signal.

An advantage of the present invention is that it permits a circuitsystem (preferably having pulse width modulation) for activating theexcitation winding and delivering electric power for the excitationwinding to be operated virtually in the stand-by mode.

The EMC measures may be reduced because in the holding state only theelectric power for the idling power of the circuit must be provided. Incomparable magnet systems, the power is cyclical in the holding state,whereby interference fields cannot be avoided. The cutout power isminimal. The holding power is low and corresponds to the standby powerof the control electronics. The design of the electronics is determinedonly by its own power consumption. From the point of view of power, themagnetic circuit is designed only for the “close magnet armature”situation. The cutout power should preferably be ensured in the pull-inphase, for example, by charging a capacitor during the pull-in phase. Asis the case in comparable systems, the permanent magnet is made of amagnetically hard material, for example, of AlNiCo, rare earth compoundsbeing also utilizable.

The advantage of the magnet system is in particular that less space isneeded for the excitation coil, permitting a more compact design.

The present invention may be used in general wherever the motion of themagnet armature is convertible into the form of a linear drive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be elaborated upon below based on exemplaryembodiments with reference to the drawings, in which:

FIG. 1 shows a schematic diagram of an electromagnet system having apulled-in magnet armature;

FIG. 2 shows a schematic diagram of an electromagnet system having alifted magnet armature; and

FIG. 3 shows a perspective view of an electromagnet system as anassembly drawing.

DETAILED DESCRIPTION

Magnet yoke 10 has a U shape and has two symmetric halves (in an Lshape) with respect to the vertical axis of symmetry SA with longer polelegs 11 and short cross legs 12. The cross legs are facing each other. Apermanent magnet 20 is mounted between the cross legs. For this purpose,the ends of the cross legs have projections 19, between which thepermanent magnet is clamped during assembly. In contrast to comparablemagnet constructions, where expensive laser welding joints are used,this is an elegant and simple construction. FIG. 3 shows the assemblydrawing, where it can be seen that the magnet system is made of sheetmetal stacks which are riveted through cover plates 80, resulting inmechanical cohesion.

The free ends of pole legs 11 form a plane as pole faces for magnetarmature 60. Magnet armature 60 is made of a plate-shaped body havinglateral extensions 61. A restoring force is applied to the magnetarmature, which should be preferably linearly movable, by at least onespring 51. The magnet armature has an air gap or stroke 18. A mechanicallink 52 exists between the magnet armature and a contact apparatus 53 ofthe switch or contactor 54.

The magnet yoke has its usual form as a sheet metal stack. Fasteninglegs 41, each having a bore hole, to which the magnet system may beattached in a housing, are situated laterally, facing cross legs 12.

A magnetic shunt circuit MK2, present on magnet yoke (11, 12) facingaway from the pole faces, is associated with first magnetic flux circuitMK1. The shunt circuit is formed by two second yoke arc legs 24(parallel legs) parallel to short cross legs 12. Cross legs and yoke arclegs are separated by a groove; otherwise they are material componentsof the magnet yoke.

Each pole leg 11 is surrounded by bobbins having excitation windings 30,32. The magnetic flux generatable by excitation windings 30, 32 issuperimposed in the air gap on the magnetic flux of permanent magnet 20.During the pull-in operation, the two magnetic fluxes are subtractedfrom each other in the shunt circuit.

Yoke arc legs 24 each have a smaller cross-section compared to firstcross legs 12 and the magnet armature.

However, due to its function, during the pull-in operation, the highestmagnetic flux density is in the magnet armature.

The yoke arc legs are separated by a remanence air gap 25. The width ofthe remanence air gap is approximately 0.3 mm. The ratio of magneticflux MK1 to magnetic flux MK2 is defined by the cross sections of theyoke arc legs and the width of the remanence air gap.

Due to its magnetic energy, the permanent magnet generates a magneticflux, which is split into the two magnetic flux circuits MK1 and MK2.The design of the magnet system, in particular the strength of thepermanent magnet, is selected such that in the holding state (magnetarmature pulled in, without being acted upon by the electric excitationvia coils 30, 32) the magnet armature is held securely on the magnetyoke for all operating conditions.

Using this magnetic dimensioning, no magnetic power needs to bedelivered by the excitation coils in the holding position; the holdingforce for the magnet armature is applied by the permanent magnet alone.This preferably makes it possible to minimize the electric power of theassociated electronic circuit, because essentially only the triggeringpower is to be provided. The low triggering power may be adequatelysupplied, for example, by a suitably dimensioned accumulator capacitoror an inductor whose energy content may also be monitored by theelectronic circuit.

It only requires a low power to move the magnet armature from theholding position to the open position (which may mean the OFF positionof a switch, for example). This power is delivered by the controlelectronics to excitation windings 30, 32, whose magnetic flux weakensthe flux through the pole faces to the point where the holding force isovercome.

The flux pattern changes accordingly, and the major portion of themagnetic power is forced into the shunt circuit (yoke arc leg 24,remanence air gap 25). An accumulator capacitor may be used for cutout,because a power of maximum 1 Watt is sufficient for this purpose. Such acapacitor has no significant power loss, so that only an idling power onthe order of magnitude of considerably less than 1 Watt must be providedin the electrical trigger circuit system in the holding state.

The magnet system is driven (closing of the magnet armature, driveexcitation) by a strong coil current (e.g., 100 Watt for 100 msec.)which generates a magnetic flux opposing that of the permanent magnet inthe pole legs and also overcomes the spring force at the magnetarmature. As the magnet armature approaches the pole faces, the densityof the magnetic field in magnetic circuit MK1 increases. Magnetic shuntcircuit MK2 now only contains a low magnetic energy.

After contact of the magnet armature with the pole faces (closing), thepower flow may be turned off because (as explained above), the holdingforce is provided statically.

1. An electromagnet system for a switch, comprising: a main magneticcircuit including a magnet yoke and a magnet armature, the magnetarmature being acted upon by a restoring device and being mechanicallylinked to a contact apparatus of the switch; at least one permanentmagnet disposed in the main magnetic circuit and configured to generatea holding force for the magnet armature; a shunt circuit including aplurality of pole legs and a yoke arc of the magnet yoke, the yoke arcfacing away from pole faces of the magnet yoke and being interrupted bya remanence air gap, the magnet armature being capable of contacting thepole legs so as to close the main circuit, the shunt circuit beingparallel with the main magnetic circuit so that the permanent magnet isa magnetic energy source for the shunt circuit; a circuit systemconfigured to electrically trigger the electromagnet system and to beoperated in a stand-by mode when the magnet armature contacts the polelegs; and at least one excitation winding respectively associated withat least one of the pole legs, an electromagnetic force of the at leastone excitation winding being configured to generate a pull-in force forthe magnet armature; wherein the electromagnet system is magneticallydimensioned such that a minimum magnetomotive force of the at least oneexcitation winding delivered by an energy accumulator to force amagnetic power of the permanent magnet into the shunt circuit issufficient for opening the electromagnet system.
 2. The electromagnetsystem as recited in claim 1 wherein the electromagnet system is for aswitch contactor.
 3. The electromagnet system as recited in claim 1wherein the pole legs are connected via cover plates.
 4. Theelectromagnet system as recited in claim 1 wherein the magnet yoke has aU-shape and includes a first and a second L-shaped halve, each L-shapedhalf including a respective pole leg and an associated respective crossleg, each respective pole leg being longer than the associatedrespective cross leg, each respective pole leg facing a respectivecontact face of the magnet armature.
 5. The electromagnet system asrecited in claim 4 wherein the permanent magnet is disposed in a centralportion of the magnet yoke between the cross legs and is held byclamping.
 6. The electromagnet system as recited in claim 4 wherein theyoke arc is disposed parallel to the cross legs.
 7. The electromagnetsystem as recited in claim 4 wherein the permanent magnet is clampedbetween the cross legs.
 8. The electromagnet system as recited in claim1 further comprising a non-magnetic material disposed in the remanenceair gap.
 9. The electromagnet system as recited in claim 1 furthercomprising a magnetic sheet system.
 10. The electromagnet system asrecited in claim 1 wherein the energy accumulator is an accumulatorcapacitor.
 11. The electromagnet system as recited in claim 1 whereinthe energy accumulator is an inductor.